[600MRG] [rsgb_lf_group] Receiver protection

Mel Farrer farrerfolks at yahoo.com
Tue Jul 10 15:01:34 EDT 2018 

The real solution is "sequence keying",  PTT Preamp off with relay or pin diode input to ground ( I use both), same contact closure key amplifier, contact closure keys transmitter to on.  Reverse unkeys transmitter first then cascades down with preamp on last. There are others, but this is mine.
Mel, K6KBE

      From: David G0MRF via 600MRG <600mrg at mailman.qth.net>
 To: rsgb_lf_group at yahoogroups.co.uk; rsgb_lf_group at blacksheep.org; lowfer at mailman.qth.net; 600MRG at mailman.qth.net 
 Sent: Tuesday, July 10, 2018 11:44 AM
 Subject: Re: [600MRG] [rsgb_lf_group] Receiver protection
   
 Hi Paul
I'm sure you will get many good ideas from the group.I took the view that my preamp protected the receiver....and the preamp was expendable. - Also the max output from the preamp was not sufficient to damage the receiver.
Even so....After using it for a while, I decided that a little more protection was called for, so I placed a small relay (about 1/2 inch square) to short the input to the preamp to ground when the system was in 'transmit'

73
David
 
 
-----Original Message-----
From: N1BUG paul at n1bug.com [rsgb_lf_group] <rsgb_lf_group at yahoogroups.co.uk>
To: rsgb_lf_group <rsgb_lf_group at blacksheep.org>; rsgb_lf_group <rsgb_lf_group at yahoogroups.co.uk>; Discussion of the Lowfer (US, European, & UK) and MedFer bands <lowfer at mailman.qth.net>; 600MRG <600MRG at mailman.qth.net>
Sent: Tue, 10 Jul 2018 12:05
Subject: [rsgb_lf_group] Receiver protection

    Does anyone have ideas for receiver front end protection at LF and
MF? I am worried about my TX signal damaging receivers.

Of course the best idea is to disconnect the RX antenna from the
receiver while transmitting. Any good solution while leaving it
connected?

Now I have a pair of back to back 1N4148 diodes across the receiver
front end but I don't think this offers real protection because they
allow too high voltage before conducting. Also there is a preamp
after the didoes which can bring the RF to dangerous levels!
(Somehow nothing was damaged during last winter operating this way... :)

73,
Paul N1BUG

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